If you turn on a light at night in the mountains of Papua New
Guinea, says Paul Hebert, you will collect some 2,000 species of
moth. Moving up the mountain a bit will net you a different but
equally daunting crowd. As a young postdoc in the 1970s, Hebert,
now an evolutionary biologist at the University of Guelph in Ontario,
spent five years trying to make sense of that fluttering confusion,
before finally deciding it was beyond his or any human’s capacity.
For two decades after that he retreated to water fleas, of which
there are only 200 species. Then in 2003 he did something new.
In a paper that year he began by describing the diversity of life as
a “harsh burden” for biologists, and proceeded to suggest some
relief: Every species on Earth could be assigned a simple DNA bar
code, Hebert wrote, so it would be easy to tell them apart.

The bar code Hebert suggested is part of a gene called CO1,
which helps produce the energy-carrying molecule ATP. CO1 is
so essential that every multicellular
organism has it. But there is enough variation in its
sequence—each of the 600-odd spots in the bar
code region can be filled by any of four different
DNA bases—that two species rarely have the exact
same one. Such differences in a gene are readily
scanned by machine even when the animals
themselves might confound an expert; Hebert’s
group is now sequencing a thousand specimens
a day. They’ve bar coded nearly 40,000 species
of moth and butterfly already. The technique has
commercial as well as scientific promise. Mislabeling
of fish on menus is rampant, it turns out.